A file server is a computer that provides file service relating to the organization of information on storage devices, such as disks. The file server or filer includes a storage operating system that implements a file system to logically organize the information as a hierarchical structure of directories and files on the disks. Each “on-disk” file may be implemented as a set of data structures, e.g., disk blocks, configured to store information. A directory, conversely, may be implemented as a specially formatted file in which information by other files and directories is stored.
A filer may be further configured to operate according to a client/server model of information delivery to thereby allow many clients to access files stored on a server. In this model, the client may comprise an application, such as a database application, executing on a computer that connects to the filer over a computer network. This computer network could be a point to point link, a shared local area network (LAN), a wide area network (WAN) or a virtual private network (VPN) implemented over a public network such as the Internet. Each client may request the services of the file system on the filer by issuing file system protocol messages (typically in the form of packets) to the filer over the network.
The disk storage typically implemented has one or more storage “volumes” comprised of a collection of physical storage disks, defining an overall logical arrangement of storage space. Currently available filer implementations can serve a large number of discrete volumes (150 or more, for example). Each volume is generally associated with its own file system. The disks within a volume/file system are typically organized as one or more groups of Redundant Array of Independent (or Inexpensive) Disks (RAID). RAID implementations enhance the reliability and integrity of data storage through the redundant writing of data stripes across a given number of physical disks in the RAID group, and the appropriate caching of parity information with respect to the striped data. In the example of a WAFL-based file system and process, a RAID 4 implementation is advantageously employed. This implementation specifically entails the striping of data across a group of disks, and separate parity caching within a selected disk of the RAID 4 group.
The physical disks are often connected to a switching network. This switching network may take the form of Fibre Channel switches connected to fibre channel loops, with each loop having a number of disks connected thereto. By utilizing a number of interconnected switches, a switching fabric can be created. This fabric allows any individual filer to have access to, subject to ownership limitations, any disk connected to the switching fabric; however, only the filer that “owns” a disk can write to that disk. One methodology of ownership of disks within a network storage environment, such as a switching fabric, is described in U.S. patent application Ser. No. 10/027,020 filed on Dec. 21, 2001 entitled SYSTEM AND METHOD FOR TRANSFERRING VOLUME OWNERSHIP IN NETWORKED STORAGE by Joydeep sen Sarma et al, which is hereby incorporated by reference. Another methodology is described in U.S. patent application Ser. No. 10/027,457 filed on Dec. 21, 2001 entitled SYSTEM AND METHOD OF IMPLEMENTING DISK OWNERSHIP IN NETWORKED STORAGE, by Susan M. Coatney et al.
As part of an ownership system, each filer “knows” which disks it owns. In other words, each filer has a list of identifiers for owned disks. Additionally, each disk preferably has ownership information written to a predetermined area of the disk, defined as “sector S” in the aforementioned patent application. This disk ownership information may be a unique serial number for the owning filer. However, the need can arise when other filers require, in place of the filer serial number, a resolvable address name, i.e. a name that can be resolved into a network address using an appropriate technology such as is the Domain Naming Service (DNS). To distribute these resolvable names, filers currently broadcast the address information in a data packet to all devices connected to the switching fabric.
Additionally, it is often required to take individual disks offline for a period of time. For example, the disks may be receiving a firmware upgrade. If a file server attempts to access an inaccessible offline disk, data loss can occur. It is, thus, preferable that each filer connected to a switching fabric be able to determine which disks are offline and inaccessible, thereby avoiding data loss. A current method to distribute this information employs the sending of a multicast data packet to all of the filers on a switching fabric containing a list of disks that are offline and inaccessible.
A noted disadvantage of the multicast method of distributing these types of data is a need to ensure that all filers receive any updated information. For example, if a filer is offline when a packet is broadcast, the filer will not receive the data. If the filer subsequently comes on-line, and attempts to access an offline and inaccessible disk, the data may be lost. Similarly, if a filer is offline when a resolvable name is broadcast, but then comes on-line, that filer will not know the address resolvable name. File servers can be programmed to regularly re-broadcast this data, but a filer still needs to wait until the next broadcast to receive this information.
Thus, it is an object of the invention to provide a system and method for storing and distributing various data for use by the devices connected to a switching fabric without the need for multicasting data packets.